So you blame a running back, or take away credit from one, because Denver signed/drafted players who are good? That isn't fair to him or any RB in that situation. Besides, running backs that are successful benefit from good OL play and WRs/TEs who can block/catch passes can't they?
Let's take a look at the guys you mentioned. Moreno didn't have more rushing TDs than Peterson (they tied at 10). But Peterson had 38 more carries and was the focal point of Minnesota's offense and for Moreno to match his TD total is something to look at.
Matt Forte. 48 more carries and roughly 300 more yards. Good numbers for him. Multiply Moreno's ypc and the 48 times he rushed less and he would've finished with about 100 yds less than Forte. Forte is a good RB.
Frank Gore. 35 more carries and 90 more yards. Everything you said that takes away from Moreno's season can be said for Gore right? Mobile and good QB, good TE in Davis, good WRs in Boldin and Crabtree. Also one of the best defenses in the league.
Lesean McCoy. Top 3 RB in the league IMO. He can run and catch. His 1,607 yds on the ground showed how valuable he is in Chip Kelly's system.
To conclude, I'm not saying Moreno is a Top-5 RB. What he is though is an upgrade over Miller/Thomas. If we could agree on that then alright. If Moreno gets hurt again, lean on Miller and a rookie RB that Miami still drafts (which is what I want them to do).